This invention relates to winches having a rotatable drum with drive means for reeling in and releasing a cable or the like. More particularly the invention relates to winch mechanisms in which the drum is driven and controlled by means of fluid pressure-operated clutches and brakes.
An advantageous form of winch mechanism for disposition on a vehicle or elsewhere has an input clutch for selectively transmitting drive from an engine to a rotatable drum and further includes a disconnect clutch for enabling the drum to turn independently of the drive mechanism and also has a brake for selectively immobilizing the mechanism. The input clutch is spring-biased to a disengaged position and engages in response to fluid pressure. Both the disconnect clutch and the brake are spring-biased to engaged positions and are disengageable in response to fluid pressure.
A control valve provides for the selective application of fluid pressure to particular ones or combinations of the clutches and brake to establish any of four operational modes of the winch. These include a Reel-In mode at which the input clutch and also the brake are pressurized and a Brake-On mode at which both clutches and the brake are unpressurized to immobilize the drum. At a Brake-Off mode, only the brake is pressurized enabling a load to pull out cable against the drag of the drive mechanism. At a Disconnect mode, the brake and disconnect clutch is pressurized thereby enabling the drum to be turned freely independently of the drive mechanism so that cable may be withdrawn manually without undue effort.
Difficulties may be encountered in winch mechanisms of this general type at the particular times when the control valve is shifted into the Reel-In position particularly if valve movement into this position occurs slowly. At that time modulated rising fluid pressures are directed to the input clutch through one flow line and to the brake through another flow line. The resulting engagement of the input clutch and disengagement of the brake should be precisely synchronized. If the input clutch engages before the brake releases, drive line shocks, accelerated wear and in extreme cases stalling of the driving engine may occur. If the input clutch engagement is delayed relative to brake relase, a load which may be pulling on the cable may drop abruptly and excessive cable may be withdrawn giving rise to cable slack and other adverse effects. Essentially similar problems may be encountered when the control valve is shifted away from the Reel-In position.
Resolution of this problem is made difficult since pressurized fluid must be applied to the brake at certain modes of operation where it is not applied to the input clutch. This dictates the providing of separate flow lines from the control valve to the input clutch and to the brake. The control valve and fluid lines must then be precisely balanced with respect to providing synchronized pressure increases and decreases to the input clutch and brake if the problems discussed above are to be avoided.
A winch mechanism of the general type to which the invention relates is disclosed in copending U.S. application Ser. No. 662,320 of L. F. Yates et al, filed Mar. 1, 1976, for WINCH WITH FREE WHEELING DRUM and assigned to the assignee of this application, said copending application being a continuation-in-part of application Ser. No. 334,354 filed Feb. 21, 1976, and now abandoned.